Perennial Grasses Prevent Nitrate Leaching on a Sandy Loam Following Swine Manure Application.

When nitrate is lost below the root zone, the potential exist for degradation of ground water quality with serious health implications. The study was conducted between 2009 and 2013, with cropping system, perennial versus annual, as the main plot and manure nutrient management system, as the subplot. The perennial cropping system consisted of a mixture of timothy and orchard grass and the annual crop was a rotation of barley and canola. After 4 years of establishment, the grasses in the perennial plots was ploughed under at the end of 2012 growing season and both annual and perennial plots were cropped to canola in 2013. Soil samples were taken three times during the growing season, in the spring, midseason and harvest. Leachate samples were collected from filed core lysimeters within each plot after snowmelt and intermittently based on rainfall events. Soil, plant and water samples were analyzed for nitrogen and phosphorus. A major finding of this study was that the annual cropping system lost substantially more nitrogen (20 to 60 kg ha^-1 of N) through nitrate leaching than the perennial system (~1 kg ha^-1 of N). These differences could not be attributed to differences in nitrogen removal as the annual crops sometimes took up more nitrogen than the perennial. The lack of nitrate leaching from the perennial system may be due to better synchrony between available nutrients and crop removal, greater underground biomass nitrogen and greater soil water use by the perennials.